In the beginning, dive watches were pure tools: essential swimming buddies that helped keep divers on time and hence, well, alive. Today they’re something else: fashion statements, conversation pieces, rugged companions for a trip to the beach or pool. This is an excerpt from Timeline: “Dive Watches Through the Decades,” which traces the history of the dive watch from its start in the 1920s, with the invention of the first truly water-resistant cases, to 2014. (It includes only mechanical watches.*)